How to redirect a user to a specific site when connected to a router?

Question

Computer networks

Hello again.
Somehow in one organization I saw how a local admin set up a router in such a way that when users first connect to it (when the Internet is opened, when turned on in the DHCP server, maybe something else) the user was immediately thrown to a specific site (in this case, the resource of the organization ).
Can anyone tell me how these things are done. It would be very convenient for users to come to the workplace and turn on the computer to see some html page with an important announcement for the organization, etc.

Answer 1

The keyword is "captive portal".

Answer 2

I implemented this in restaurants with the help of Mikrotiks. Done in minutes. Google "Mikrotik Hotspot" - a lot of topics on how to set up a router.